Answer:
Ailerons are control surfaces on a wing that increase or reduce lift. There is one on each wing, and they operate in difeerent direction: when one goes up, the other goes down (and vice-versa). Ailerons allow an aircraft top bank, which then lets the 'plane turn.
Unlike in a boat, the pilot does NOT use the rudder to turn the plane; the rudder is there just to balance the turn, to prevent yaw or skidding.
"Aileron" is a french word meaning "little wing".